System and method for improving video recorder performance in a search mode

ABSTRACT

A method and apparatus wherein video images are recorded on a plurality of tracks of a tape such that, for playback in a search mode at a speed higher than the recording speed, the displayed image will consist of a plurality of contiguous parts, some of the parts being read out from tracks each having a different frame recorded thereon.

This is a continuation of application Ser. No. 08/581,882, filed Jan. 2,1996, abandoned, which is a continuation of application Ser. No.08/204,904. Filed Mar. 2, 1994, abandoned, which is a continuation ofapplication Ser. No. 07/865,525, filed Apr. 9, 1992, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention applies to video recorders and, specifically, tovideo recorders operative with playback at the recording speed and atleast one other speed.

2. Description of the Related Art

The problem of creating adequate pictures or images from a videorecording played back at the recording speed, and one or more higherspeeds in a search mode has been addressed before. It is discussed in apublication entitled "Introduction to the 4:2:2 Digital Video TapeRecorder" by Stephen Gregory of the Sony Broadcasting Company, publishedby Pentech Press, London, 1988. Chapter 7 teaches a method ofpixel-based shuffling for improving the robustness of the system and forrecovering pictures in multispeed modes. Briefly, arrays are formed ofpixels whose position has been scrambled. The position of the arrays isthen scrambled, first within a field and subsequently over fourconsecutive fields.

This is a very complicated method and yields reasonable results at highspeeds, but decreases the picture quality at the lower search speeds.Further, no data compression takes place.

SUMMARY OF THE INVENTION

It is an object of the present invention to furnish a method and systemin which acceptable picture quality both at higher and lower searchspeeds is obtained, preferably in combination with data compression.

The present invention is a method of recording data defining a pluralityof images on substantially parallel tracks of a recording medium at arecording speed, for playback at said recording speed and at least oneadditional speed. It comprises the steps of generating a plurality ofbasic segments for each of said images in response to received imagedata, each of said basic segments defining an incremental part of animage extending in a first direction and in a second directiontransverse to said first direction.

The basic segments are recorded on the tracks as a plurality ofsub-sequences each defining a first contiguous part of the imageexceeding said incremental part in area. Sequentially recordedsub-sequences in turn define second contiguous parts of the image,greater than the first contiguous parts. All sub-sequences on one tracktogether defining a third contiguous part of the image exceeding in areasaid second contiguous part constitute a sequence. The present inventionalso constitutes a method for generating display signals for display ofan image. Bursts of data (macro-segments) are read from a recordingmedium at a selected speed exceeding the recording speed of the data.The recording medium has a plurality of tracks each having at least partof one of a plurality of sequential images recorded thereon. Each of thebursts of data comprises data defining a contiguous area of one of theimages, while a plurality of bursts varying in number in correspondenceto the ratio of the selected speed to the recording speed defines allparts of an image.

The data of the read-out bursts is stored in a memory until theplurality of bursts has been received, and then read from the memory ina sequence and at a rate suitable for display, thereby creating thedisplay signals.

The present invention further constitutes a recording medium having aplurality of tracks, a plurality of images being recorded on the tracks,each of said tracks having a data sequence defining a first contiguousarea of one of the images, said sequence comprising a plurality ofsequentially recorded sub-sequences each defining a second contiguousarea smaller than that first contiguous area, each of said sub-sequencescomprising a plurality of sequentially recorded basic segments eachdefining a third area of said image, the plurality of third areastogether constituting one of the second areas.

The present invention also constitutes an apparatus for recording videosignals defining a plurality of images on a plurality of tracks of arecording medium for replay at the recording speed and at least onehigher speed. Coding means are provided for encoding said video signalsinto basic segments each basic segment defining an incremental area ofone of said images.

Memory means store a plurality of said basic segments, addressing meansreading out a plurality of sub-sequences, each comprising basic segmentsdefining contiguous parts of said image, from said memory means in apredetermined order, thereby furnishing read-out sub-sequences.Recording means record the read-out sub-sequences on tracks of therecording medium.

During playback at a speed exceeding the recording speed, only part ofthe data on each track will be read out. Of this, only a part will havea SNR sufficiently high for use in an error correcting code. This latterpart is called a macro-segment herein.

The present invention also constitutes an apparatus for furnishingdisplay signals in response to macro-segments of data read from arecording medium at a speed different from the recording speed. Itcomprises means for storing the macro-segments together constituting animage, and means for reading out the stored data in a sequence and at arate suitable for application to display means.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, its operation and further advantages thereof willbe further clarified in the following description of preferredembodiments when taken in conjunction with the drawings, in which

FIG. 1a is a schematic diagram showing track pairs and head pairs inazimuth recording;

FIG. 1b is a diagram showing the variation of signal-to-noise ratio withhead position in FIG. 1a;

FIG. 2 is a diagram illustrating the head vs. track movement at aplurality of speeds exceeding the recording speed;

FIG. 3 is a diagram illustrating a problem which arises for anunacceptable ratio of playback speed to recording speed;

FIG. 4 is a schematic diagram illustrating head vs. track movement at anacceptable speed higher than the recording speed;

FIG. 5a illustrates the composition of a basic segment;

FIG. 5b shows an image divided into macro-segments and basic segments;

FIG. 5c is a schematic diagram illustrating tape tracks having thesegments of FIG. 5b recorded thereon;

FIG. 6 illustrates macro-segment bursts recoverable at 2.5 times therecording speed according to the system and method of the presentinvention;

FIG. 7 illustrates the corresponding reconstructed image; and

FIG. 8 is a block diagram of the recording and playback system accordingto the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The problem to be solved by the present invention is to furnish a videorecorder/playback system and method which yields the best possibleimages for playback at the recording speed as well as at higher speeds,during, for example, a search mode. The solution to this problem inaccordance with the present invention will be analyzed based on apreferred embodiment in which azimuth recording is used, i.e., theinformation is recorded on neighboring tracks with opposite azimuth.This is illustrated in FIG. 1a where the two neighboring tracks aredenoted by a and b, respectively, and information is recorded and readfrom the track pairs by a head pair A, B. As is well-known, the gap inhead A is so oriented that it can only read information from the atrack, while head B can read information only from the b track. In thepreferred embodiment, it is also assumed that the width of the head isequal to the width of the track and that there are 6 tracks, i.e. 3track pairs, per frame. The track pairs are numbered 1, 2, 3 etc. inFIG. 1a.

Again referring to FIG. 1a, the head pair AB will, during recording, andduring playback at the recording speed, travel along the tracks so thatthe highest signal-to-noise ratio is always obtained. However, at ahigher playback speed, the heads will not travel parallel to the tracks,but will take the paths illustrated in FIG. 1a by two solid lines, onefor head B and one for head A. These paths involve the crossing oftracks and, therefore, a variation of the signal-to-noise ratiofurnished by the heads as a function of position. This variation isillustrated in FIG. 1b with a solid line for head A and a dashed linefor head B. For any particular application, there is a minimum value ofthe amplitude plotted in FIG. 1b (SNR) required to detect bits with anerror rate that can be handled by the error correction coding system.

For a simplified model assuming perfect linear tracks and heads with aneffective width equal to the track width, the direction of head motionas a function of the multiple of the recording speed at which playbackoccurs, is shown in FIG. 2. Also, as illustrated in FIG. 2, the headpair is preferably not in its recording or normal playback position atthe start, but is located so that the center of head A coincides with 5the edge of the track, i.e., in a position where the SNR is justsufficient to start data recovery. This change in relative position ofhead to tape takes place automatically, simultaneously with selection ofa search mode by the user, and minimizes track crossings. With thispositioning, no track crossings occur at twice the recording speed, onecrossing occurs at 3 times the recording speed, etc. At a playback speedof p×v0, where p is the speed ratio and v0 the recording speed, eachdata burst is 1/(p-1) of a tracklength long. Since only a fraction f ofa data burst can be used, the usable data part when track crossing isinvolved is f×1/(p-1) at a playback speed which is p times the recordingspeed. For f=1/2, the usable data is 1/[2(p-1)].

The macro-segments derived from sequential tracks are to be stored inmemory, and subsequently read-out from memory for application to a videodisplay system to recreate a whole image. As discussed above andillustrated in detail in FIGS. 3 and 4 for different playback speeds,only part of the information recorded on each track can be read out atsuch higher-than-recording (search) speeds. Therefore, even after alltracks associated with a given frame of the video signal have beenscanned, some parts of the image (indicated by blank track portions intracks 1-6 of frame n) are still missing. According to the invention,the corresponding parts of subsequently received frames, recorded onsubsequent tracks, are to be used to fill in the missing parts. As isillustrated in FIG. 3, (for f=1), this cannot be accomplished when theplayback speed is three times the recording speed. Only the first partof tracks 1 and 4 is read, while the middle part of tracks 2 and 5 andthe last part of tracks 3 and 6 are read for all frames. The other partsof the tracks are never scanned. The reason for this is that p is anintegral (sub)multiple of the number of tracks per frame: N/p=6/3=2. Onthe other hand, as illustrated in FIG. 4, at a playback speed which isfive times the recording speed, all parts of each track will be readwithin five sequential frames. It is thus a requirement that any speedfor quick search be such that neither N/P nor P/N is an integer.

According to the invention, data is recorded on the tape in such a waythat each of the above-mentioned macro-segments defines a horizontallyand/or vertically contiguous part of the image, each part being assquare as possible. The recording is also such that a macro-segment,i.e., data defining a contiguous image portion, is read out from eachtrack at different quick-search speeds, the only difference being thatthe higher the quick-search speeds, the smaller the amount of datawithin a macro-segment and, therefore, the larger the number ofmacro-segments per displayed frame. Readout from storage for displaypurposes proceeds in the normal line-by-line scanning pattern. Thisrecording scheme will now be discussed in greater detail with referenceto FIGS. 5 and 6.

Referring first to FIG. 5a, this illustrates the basic segments of whichthe image is constructed in a preferred embodiment. Each basic segmentcontains sixty discrete cosine transform (DCT) encoded blocks of 8×8pixels, all the blocks inside of the segment being adjacent blocks inthe image. Each basic segment contains luminance blocks, Y, associatedwith 4 block lines and 10 block columns, as well as the correspondingchrominance blocks (UV). The exact structure of the basic segments withrespect to the number of pixels and the type of coding is not importantto the present invention. Even a single block could be used. Also, theblocks can be encoded in a variable or fixed word-length format. Thelatter is used for convenience in the preferred embodiment. Withvariable word-length coding, the block-length will tend to average out:alternatively, the number of bits per basic segment, or per sequence orsub-sequence can be fixed. A wide variety of embodiments will be readilyapparent to one skilled in the art. However, a contiguous area of theimage to be displayed is always represented in each basic segment.

Referring now to FIG. 5b, the illustrated rectangle represents one frameof a received video signal. The word "frame" as used herein can alsoinclude a field, since a field can be considered as a frame with lowerresolution. The image represented in the frame is first divided intothree horizontal sections A, B, C. Each of these sections containsfifty-four basic segments. Reference to FIG. 5c shows that thefifty-four basic segments associated with each of the horizontalsections are recorded on respective track pairs, i.e., constitute a"sequence" as defined herein. The order in which recording takes placeis indicated by the numbering of the basic segments in FIG. 5b, i.e., itis carried out in a column-by-column basis, each column containing 6vertically adjacent basic segments, constituting a "sub-sequence".

Close examination of this type of block shuffling shows that, asdiscussed above, it yields macro-segments of adjacent blocks at aplurality of speeds exceeding the recording speed. Also, since thelength of each basic segment exceeds its height, column-by-columnrecording results in macro-segments which are as square as possible.

As will be shown below with reference to FIGS. 6 and 7, one-third of atrack and, therefore, for the given embodiment, one-ninth of the frameconstitutes a macro-segment at playback at two and a half times therecording speed. At five and a half times the recording speed, one-ninthof the track, namely, columns of six vertically adjacent basic segments,constitute a macro-segment, etc. Playback speeds at which a non-integralnumber of basic segments per macro-segment would be required would notresult in optimum picture quality. For example, at five times therecording speed, one-eighth of a track or one-eighth of fifty-four basicsegments would constitute a macro-segment. This playback speed shouldpreferably not be chosen even if it meets the N/p requirement specifiedabove.

For a specific illustration of the reconstruction of the image from themacro-segments read from the tape at two and a half times the recordingspeed, reference is made to FIGS. 6 and 7. In FIG. 6, sequential framesare indicated by "fr 1", "fr 2", etc. Above the frame notation are thetrack pairs associated with each frame, namely, 1, 2 and 3. The trackareas from which usable information is read out when the playback speedis two and a half times the recording speed, are indicated by horizontallines and are numbered in the order of read-out.

FIG. 7 shows how the data read out from the indicated track areas is puttogether in memory to constitute the image. Track area 1 of FIG. 6, forexample, contains information corresponding to the left-most imageportion of track a of FIG. 5b and, thus, the corresponding part of theimage in FIG. 7. Next, the right-most portion of track 2 is read out,resulting in the filling in of the image portion labelled 2 in FIG. 7.No portion of the third track of frame 1 can be read-out, the nextavailable macro-segment being the middle portion of the first track offrame 2, which results in the addition of the image portion marked 3 inFIG. 7. The readout continues until the middle area of track 2 of frame5 is read-out. This completes the image by furnishing data required toreconstruct its central part. While it is true that the parts of theimage are not all derived from the same frame, this will make nodifference if a still picture is concerned. If there is movement fromframe to frame, the errors which are created are not visually toodisturbing because the probability of motion occurring within a blockwhich has both horizontal and vertical dimensions is quite high and thevisually, particularly disturbing artefacts created by a constant erroralong a horizontal or vertical line extending all along the image areavoided.

One embodiment of apparatus required to carry out the present inventionis illustrated in FIG. 8. For recording, a video camera 20 is provided.The output of video camera 20 is applied to an analog-digital converter22. The digitized information at the output of analog-digital (A/D)converter 22 is stored in a memory 24 to allow formation of the 8×8pixel blocks by use of address control AC. The blocks are encoded by adiscrete cosine transform (DCT) in a transform stage 26 as shown, e.g.,in Europen Patent Application EP 0 286 184 filed Jun. 4, 1988 andpublished Dec. 10, 1988 corresponding to U.S. Pat. No. 4,881,192. Othercodes could be used. In any event, data compression takes place. Theaddresses and amplitudes constituting the DCT blocks are again stored,(M2, which may be part of M1) to allow readout as basic segments in theorder required for recording the desired sub-sequences illustrated inFIGS. 5b and 5c on a tape 30 by a recording head 32.

For display, the data on the tape is read out by a read head 34. Thespeed at which the readout takes place is controlled by a speed controlSC. When readout is taking place at the recording speed, the data isapplied to a third memory 36 in the consecutive order of basic segmentsindicated in FIGS. 5b and 5c. If the readout is at other than therecording speed, namely, at a higher search speed selected to assurethat all image-bearing parts of the tape will be read, the data will bereceived in memory 36 as macro-segments shown in FIGS. 6 and 7. The datais applied to a stage 38 to perform the inverse discrete cosinetransformation. The output of stage 38 is applied, possibly via a memory40, to digital-to-analog (D/A) converter 42. The output of D/A 42 isstored in a display memory 44, which is a full frame memory, thecontents of which are displayed line-by-line on a display 46.

It should be noted that in above description, many items, such asmodulators required before recording, demodulators required afterreadout, etc., have been omitted for the sake of clarity. Othercomponents, such as the DCT coding stage, could be omitted or anothertype substituted. Memories can be combined or possibly omitted (e.g.,memory 40). Basic segments may contain data from more than one frame,etc.

Thus, the present invention has been disclosed in a preferredembodiment, but other embodiments will readily occur to one skilled inthe art and are intended to be encompassed in the following claims.

We claim:
 1. A method for recording digital data defining, on display, aplurality of images, on substantially parallel oblique tracks of alongitudinal record carrier at a recording speed, said method comprisingthe steps:(a) generating blocks of coded data, each block including aplurality of pixels defining, on display, a rectangular area of one ofsaid plurality of images; (b) combining a plurality of blocks to formbasic segments, each of said basic segments defining, on display, anincremental area of said one of said plurality of images; and (c)recording sequences of said basic segments on respective tracks, eachsequence being a plurality of sub-sequences of basic segments, eachsub-sequence defining, on display, a first contiguous part of said oneof said plurality of images consisting of a plurality of saidincremental areas lined up along a first axis, all of the sub-sequenceson a track together defining, on display, a second contiguous partcomposed of first contiguous parts of said one of said plurality ofimages lined up along a second axis orthogonal to the first axis.
 2. Amethod as claimed in claim 1, wherein said recording is azimuthrecording, and wherein in said step of recording, said sequences arerecorded on track pairs.
 3. A method as claimed in claim 2, wherein datadefining, on display, each of said plurality of images is recorded on aplurality N of track pairs, each of said sequences having data defining,on display, 1/N of said image.
 4. A method as claimed in claim 3,wherein N=3.
 5. A method as claimed in claim 1, wherein each of saidbasic segments defines, on display, an area having a longer length alongsaid second axis than along said first axis perpendicular to said secondaxis; and wherein said sub-sequences extend along said first axis.
 6. Amethod as claimed in claim 5, wherein said second axis is in ahorizontal direction and said first axis is in a vertical direction, andwherein said sub-sequences comprise columns of basic segments havingdata defining, on display, vertically adjacent image elements.
 7. Methodfor generating display signals for display of an image in response todigital data read from a longitudinal record carrier having a pluralityof oblique tracks, digital data for creating a plurality of imageshaving been recorded on said tracks, each of said tracks having asequence defining, on display, a first contiguous area of one of saidplurality of images recorded thereon, said sequence comprising aplurality of sub-sequences each defining, on display, a secondcontiguous area of said one of said plurality of images, the secondcontiguous areas being lined up along a first axis, each of saidsub-sequences comprising a plurality of basic segments each defining, ondisplay, an incremental area of said one of said plurality of images,the incremental areas being lined up along a second axis orthogonal tosaid first axis, each basic segment consisting of blocks of coded dataincluding a plurality of pixels defining, on display, a rectangular areaof said one of said plurality of images, at a selected speed exceedingthe recording speed, said method comprising the steps:reading outportions of data from the tracks, each portion of data representingsequentially recorded sub-sequences defining, on display, a thirdcontiguous area of one said plurality of images, said third contiguousarea being greater than said first contiguous areas, all of thesub-sequences on a track together defining, on display, said secondcontiguous areas of said one of said plurality of images; storing saidportions of data in a read-out memory until sub-sequences defining, ondisplay, a whole image have been stored; and reading out image-definingdata from said read-out memory in a sequence and at a rate suitable fordisplay, thereby creating said display signals.
 8. A method as claimedin claim 7, further comprising the step:decoding said digital databefore creating said display signals.
 9. A method as claimed in claim 8,wherein the digital data forming each of the plurality of images on saidlongitudinal record carrier was recorded on a plurality N of saidtracks, and in said method, said selected speed is a multiple p of saidrecording speed, and wherein p/N is not an integer.
 10. Apparatus forrecording digital data defining, on display, a plurality of images onsubstantially parallel oblique tracks of a longitudinal record carrierat a recording speed, said apparatus comprising:(a) means for generatingblocks of coded data, each block including a plurality of pixelsdefining, on display, a rectangular area of one of said plurality ofimages; (b) means for combining a plurality of blocks to form basicsegments, each of said basic segments defining, on display, anincremental area of said one of said plurality of images; and (c) meansfor recording sequences of said basic segments on respective tracks,each sequence being a plurality of sub-sequences of basic segments, eachsub-sequence defining, on display, a first contiguous part of said oneof said plurality of images consisting of a plurality of saidincremental areas lined up along a first axis, all of the sub-sequenceson a track together defining, on display, a second contiguous partcomposed of first contiguous parts of said one of said plurality ofimages lined up along a second axis orthogonal to the first axis. 11.Apparatus as claimed in claim 10, wherein said means tor recordingrecords the digital data forming each of said plurality of images on aplurality N of said tracks, and wherein a sequence of data, togetherdefining, on display, a contiguous fraction 1/N of said image, isrecorded on a track.
 12. Apparatus as claimed in claim 11, wherein saidsequence defines, on display, a rectangular image area extending over1/N of the height of each of said plurality of images.
 13. Apparatus forgenerating display signals for display of an image in response todigital data read from a longitudinal record carrier having a pluralityof oblique tracks, digital data for creating a plurality of imageshaving been recorded on said tracks, each of said tracks having asequence defining, on display, a first contiguous area of one of saidimages recorded thereon, said sequence comprising a plurality ofsub-sequences each defining, on display, a second contiguous area ofsaid one of said images, the second contiguous areas being lined upalong a first axis, each of said sub-sequences comprising a plurality ofbasic segments each defining, on display, an incremental area of saidone of said images, the incremental areas being lined up along a secondaxis orthogonal to said first axis, each basic segment consisting ofblocks of coded data including a plurality of pixels defining, ondisplay, a rectangular area of said one of said plurality of images, ata selected speed exceeding the recording speed, said apparatuscomprising:reading means for reading out portions of data from thetracks, each of said portions of data representing sequentially recordedsub-sequences defining, on display, a third contiguous area of one ofsaid plurality of images, said third contiguous area being greater thansaid first contiguous areas, all of the sub-sequences on a tracktogether defining, on display, a second contiguous area of said one ofsaid plurality of images; storing means for storing said portions ofdata in a read-out memory until sub-sequences defining a whole imagehave been received; and means for reading out image-defining data fromsaid read-out memory in a sequence and at a rate suitable for display,thereby creating said display signals.
 14. Apparatus as claimed in claim13, wherein on said longitudinal record carrier, the digital dataforming each of said images was recorded in a plurality N of saidtracks, wherein in said apparatus, said selected speed is a multiple pof said recording speed, and wherein p/N is not an integer.